Show that water can contain gas. Scientists hypothesize that, in
the Permian period, the world's oceans became depleted of oxygen, setting off a
chain of events leading to the Permian extinction. Students need to understand
that atmospheric gases, such as oxygen and carbon dioxide, are soluble in
water. How much of a particular gas dissolves in water depends on the
temperature of the water and on the pressure of that gas above the water. The
following demonstrations give students a direct experience with the fact that
gas can dissolve in water.

Demonstrate that water contains gas by opening a fresh bottle of carbonated
water. Students will see gas bubbles form in the water the instant you release
the pressure. And if you place a plastic bag over the top of the bottle,
students will see that it fills with gas. This gas is carbon dioxide. The high
pressure inside the bottle causes more carbon dioxide to dissolve in the water
than would dissolve at typical ground-level atmospheric pressures. In a second
demonstration, ask students if they think that tap water contains dissolved
gas. Show them a glass that you had filled with tap water the previous day.
They will see that the inside of the glass is lined with bubbles. Ask students
to explain where these bubbles came from. (The bubbles form as gas comes out
of solution. Tap water is pressurized to help it flow through the water pipes.
Pressure influences the amount of gas dissolved in water. In the open glass,
there is less pressure than in the water pipes, and some of the dissolved gases
come out of solution, forming bubbles.)

Compare how differently hot and cold water retain dissolved gas.
Temperature has a strong effect on how much gas can be dissolved in water. As
water temperatures rise, the amount of gas dissolved in the water drops. The
hypothesis explored in the segment is that the oceans warmed to the point that
they were severely depleted of oxygen. If the amount of dissolved oxygen
becomes critically low, aquatic life that requires oxygen, like fish, will die.
Scientists contend that low oxygen levels in the world's oceans at the end of
the Permian period set off a chain of events that led to the mass extinction of
95 percent of life on Earth.

Use the following demonstration to show how temperature affects the amount of
gas that can dissolve in water. (Consider having students do this activity in
small groups.) Fill a bowl three-quarters full with hot tap water and another
bowl three-quarters full with cold tap water. Fill two plastic cups halfway
with any type of carbonated soda or sparkling water. Set a cup into each of the
bowls and observe. (Make sure that the water in the bowls does not get into the
cups and that there is not so much water in the bowls that it spills out when
you put in the cups.) Ask students to compare how the water in the two cups
behaves. (In the hot water, the bubbles will be bigger and rise to the
surface more quickly than in the cold water.) In which cup will the
soda go flat first? (They both will go flat, but the soda in the hot-water
bath will go flat sooner than the soda in the cold-water bath.)

Find the site of the Siberian Traps volcanoes. Using atlases or Web
sites, such as
palaeo.gly.bris.ac.uk/Palaeofiles/Permian/SiberianTraps.html,
locate the Siberian Traps and identify the geographical area covered by lava.
As occurs in every volcanic eruption, the Traps' million-year continuous
eruptions released carbon dioxide. Discuss the climatic effects of adding huge
quantities of carbon dioxide to the atmosphere. Consider having students
research recent volcanic eruptions (e.g., Mount St. Helens, Mt. Pinatubo, and
Soufriere Hills in Montserrat) and find out how much carbon dioxide was
released. Then ask students to estimate how much carbon dioxide a million years
worth of erupting would have expelled.

After Watching

Develop a flowchart of the events that led to the Permian extinction.
Reinforce the events described in the segment. On the board, write the phrases
below in alphabetical or random order. Have students draw a flowchart, putting
events in the correct sequence.

Anaerobic bacteria thrive in the oceans and produce hydrogen sulfide as a waste product

Grow hydrogen sulfide-producing bacteria. The early Earth had little
free oxygen. Consequently, the first organisms were anaerobic, and
sulfate-reducing bacteria are among the oldest life forms on Earth. To obtain
energy, these bacteria oxidize organic matter and, in the process, produce
hydrogen sulfide, the gas that gives rotten eggs their smell. Today, these
bacteria are still common in low-oxygen environments, such as in swamps,
marshes, standing waters, and the ocean floor. Ask students if they know the
smell of mud from swamps. This mud often has a detectable sulfur odor. Hydrogen
sulfide-producing bacteria also live in the human colon. The odor of flatus is
largely due to trace amounts of hydrogen sulfide. Hydrogen sulfide is toxic to
several systems in the body, although the nervous system is most affected. The
gas stops cellular respiration by blocking oxygen from binding with
mitochondrial enzymes. Share the information in the table below with students
and have them speculate as to what concentration of hydrogen sulfide would be
required to cause an extinction on a par with the Permian extinction.

Parts
per million

Effect
of Hydrogen Sulfide on People

0.0047

People
can detect the characteristic rotten egg odor of hydrogen sulfide

10-20

Eye
irritation, sore throat, shortness of breath, and fluid in the lungs

50-100

Eye
damage

150-250

Sense
of smell deadened, making a person unaware of the danger

320—530

Fluid
fills the lungs to potentially lethal levels

530-1,000

Strong
stimulation of the central nervous system, leading to loss of breathing

800

Lethal
after 5-minute exposure

Above
1,000

Lethal
after a single breath

Collect some mud from anaerobic environments, such as roadside ditches, ponds,
swamps, marshes, or bodies of standing water. Gather the gooey sediments from a
few inches beneath the surface. A sulfur odor will tell you there are
sulfate-reducing bacteria. Put the mud in a clear container, such as a peanut
butter jar, soda bottle, or baby food jar. Add water until there is an inch of
water over the mud. Cover the container with plastic wrap and secure with a
rubber band. Put the container in a sunny spot for several weeks, adding water
as necessary. After three weeks or so, colorful colonies of bacteria will
become visible at different levels in the mud. The purple-colored ones toward
the bottom are purple sulfur bacteria and the green-colored ones below them are
green sulfur bacteria. Both produce hydrogen sulfide as a waste product.

Examine historic levels of carbon dioxide. Scientists in the segment
suggest that high levels of carbon dioxide caused major global warming that led
to the Permian extinction. Copy the following tables for students. Have them
make a line graph of the 1960-2004 data. Discuss the trend, comparing the
modern levels with the historic carbon dioxide levels measured in gas bubbles
trapped in Antarctic ice. (It is assumed that the gas in these bubbles reflects
the composition of the atmosphere that existed when the ice formed.) Use the
Antarctic ice data to calculate the average level for the past 400,000 years.
(About 222 parts per million) Discuss how levels today compare with
historic levels. (Today's are much higher) Over the past 400,000 years,
what is the range of variation in atmospheric carbon dioxide levels?
(Atmospheric carbon dioxide levels have ranged from 189.2-278 parts per
million)